1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive unlatching an actuator arm at a first spindle speed during a first spin-up mode and a second spindle speed during a second spin-up mode.
2. Description of the Prior Art
When a disk drive is powered down, a head connected to a distal end of an actuator arm is latched into a parked position to protect the head as well as the data area of the disk. The actuator arm is rotated about a pivot by a voice coil motor into the parked position where the actuator arm is typically constrained by a magnetic latch. The head may be parked on the disk, for example on an inner diameter landing zone which is typically textured to reduce stiction. When the disk drive is powered on, a spindle motor spins up the disk to an operating spin rate or xe2x80x9coperating speedxe2x80x9d which allows the disk drive to xe2x80x9csynchronizexe2x80x9d to embedded servo sectors recorded on the disk.
During the spin-up process it is desirable to unlatch the actuator arm as soon as possible and move the head over the smooth data area of the disk in order to minimize head wear caused by the textured landing zone. In prior art disk drives the actuator arm may be unlatched early in the spin-up process once the disk reaches a target speed less than the operating speed. The target speed is typically selected as the minimum speed (within a predetermined tolerance) that enables the head to fly, with stability, over the smooth data area of the disk surface. Various factors influence the target speed, including the strength of the magnetic latch, the mechanical resonances of the actuator assembly, the aerodynamics of the actuator arm and head, etc.
During the spin-up process or during the normal operating mode the disk drive may encounter an error condition, such as a momentary power loss, wherein the disk drive will latch the actuator arm back into it""s parked position. When the error condition subsides, the disk drive will attempt to xe2x80x9cre-syncxe2x80x9d by unlatching the actuator arm after the disk reaches the target speed. However, the impact of the actuator arm latching into the parked position may excite the mechanical resonances of the actuator assembly causing the head to vibrate. If the error condition subsides quickly, any residual resonance may affect the stability of the head when the actuator arm unlatches. In some cases the residual resonance will prevent the head from flying with stability at the target speed causing the head to strike the disk surface as the actuator arm unlatches during the re-sync spin-up mode. This is undesirable since it may damage the head as well as corrupt the data recorded on the disk.
There is, therefore, a need to reduce head wear in a disk drive by unlatching the actuator arm early in the spin up process while ensuring the head will fly with stability during a re-sync spin-up mode.
The present invention may be regarded as disk drive comprising a disk, a spindle motor for rotating the disk, an actuator arm, a head coupled to the actuator arm, and disk control circuitry. The disk control circuitry latches the head into a parked position when the disk drive is powered down. During a start-up process, the speed of the spindle motor is controlled to rotate the disk toward an operating speed. If the disk drive is in a first spin-up mode, the speed of the spindle motor is compared to a first target speed and the head is unlatched relative to the first target speed. If the disk drive is in a second spin-up mode, the speed of the spindle motor is compared to a second target speed and the head is unlatched relative to the second target speed. The first target speed and second target speed are less than the operating speed, and the second target speed is greater than the first target speed.
In one embodiment, the disk control circuitry comprises a microprocessor executing a control program.
In one embodiment, the first spin-up mode is a normal spin-up mode and the second spin-up mode is a re-sync spin-up mode. In one embodiment, the disk control circuitry evaluates the speed of the spindle motor at the beginning of the start-up process to determine whether the disk drive is in the normal spin-up mode or the re-sync spin-up mode.
In one embodiment, the disk control circuitry re-latches the actuator arm if a predetermined error condition is detected. The disk drive enters the re-sync spin-up mode if the error condition causes the speed of the spindle motor to fall below the second target speed. The disk drive enters the normal spin-up mode if the error condition causes the speed of the spindle motor to fall below a threshold speed less than the first target speed.
In one embodiment, the second target speed is at least five percent greater than the first target speed.
The present invention may also be regarded as a method of operating a disk drive, the disk drive comprising a disk, a spindle motor for rotating the disk, an actuator arm, and a head coupled to the actuator arm. The head is latched into a parked position when the disk drive is powered down. During a start-up process, the spindle motor rotates the disk toward an operating speed. If the disk drive is in a first spin-up mode, the speed of the spindle motor is compared to a first target speed and the head is unlatched relative to the first target speed. If the disk drive is in a second spin-up mode, the speed of the spindle motor is compared to a second target speed and the head is unlatched relative to the second target speed. The first target speed and second target speed are less than the operating speed, and the second target speed is greater than the first target speed.